linux-kernel - Re: [PATCH] Fix read buffer overflow in delta-ipc

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Message-ID: <74958ca0-e78e-0505-f738-1ddda50d8ead@st.com>
Date:   Wed, 3 Jan 2018 09:40:04 +0000
From:   Hugues FRUCHET <hugues.fruchet@...com>
To:     Andi Kleen <andi@...stfloor.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        "mchehab@...pensource.com" <mchehab@...pensource.com>
Subject: Re: [PATCH] Fix read buffer overflow in delta-ipc

Hi Andi,
Thanks for the patch but I would suggest to use strlcpy instead, this 
will guard msg.name overwriting and add the NULL termination in case
of truncation:
-	memcpy(msg.name, name, sizeof(msg.name));
-	msg.name[sizeof(msg.name) - 1] = 0;
+	strlcpy(msg.name, name, sizeof(msg.name));

Best regards,
Hugues.

On 12/22/2017 01:12 AM, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> The single caller passes a string to delta_ipc_open, which copies with a
> fixed size larger than the string. So it copies some random data after
> the original string the ro segment.
> 
> If the string was at the end of a page it may fault.
> 
> Just copy the string with a normal strcpy after clearing the field.
> 
> Found by a LTO build (which errors out)
> because the compiler inlines the functions and can resolve
> the string sizes and triggers the compile time checks in memcpy.
> 
> In function ‘memcpy’,
>      inlined from ‘delta_ipc_open.constprop’ at linux/drivers/media/platform/sti/delta/delta-ipc.c:178:0,
>      inlined from ‘delta_mjpeg_ipc_open’ at linux/drivers/media/platform/sti/delta/delta-mjpeg-dec.c:227:0,
>      inlined from ‘delta_mjpeg_decode’ at linux/drivers/media/platform/sti/delta/delta-mjpeg-dec.c:403:0:
> /home/andi/lsrc/linux/include/linux/string.h:337:0: error: call to ‘__read_overflow2’ declared with attribute error: detected read beyond size of object passed as 2nd parameter
>      __read_overflow2();
> 
> Cc: hugues.fruchet@...com
> Cc: mchehab@...pensource.com
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>   drivers/media/platform/sti/delta/delta-ipc.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/platform/sti/delta/delta-ipc.c b/drivers/media/platform/sti/delta/delta-ipc.c
> index 41e4a4c259b3..b6c256e3ceb6 100644
> --- a/drivers/media/platform/sti/delta/delta-ipc.c
> +++ b/drivers/media/platform/sti/delta/delta-ipc.c
> @@ -175,8 +175,8 @@ int delta_ipc_open(struct delta_ctx *pctx, const char *name,
>   	msg.ipc_buf_size = ipc_buf_size;
>   	msg.ipc_buf_paddr = ctx->ipc_buf->paddr;
>   
> -	memcpy(msg.name, name, sizeof(msg.name));
> -	msg.name[sizeof(msg.name) - 1] = 0;
> +	memset(msg.name, 0, sizeof(msg.name));
> +	strcpy(msg.name, name);
>   
>   	msg.param_size = param->size;
>   	memcpy(ctx->ipc_buf->vaddr, param->data, msg.param_size);
>